India is the biggest net beneficiary of money sent home by migrants:

Officially recorded remittances worldwide exceeded $232 billion in 2005, with India receiving almost 10% of the amount ($21.7 billion). China came second with $21.3 billion, followed by Mexico ($18.1 billion), France ($12.7 billion), and the Philippines ($11.6 billion). [Link]

To put this into context, remittances worldwide are roughly the same as the GDP of Sweden, and remittances to India are roughly equivalent to the entire national output of countries such as Latvia or North Korea. India makes even more foreign exchange from sending its workers abroad than it does from exporting software.[Thanks Hammer_Sickel!] Remittances to India are roughly equivalent to the entire national economic output of Latvia. India generates more foreign exchange from sending its workers abroad than it does from software exports.

International flows of labor are now becoming economically critically, like flows of capital in the decade before before:

… remittances sent through informal channels could add at least 50 per cent to the official estimate, making remittances the largest source of external capital in many developing countries. [Link]

With the number of migrants worldwide now reaching almost 200 million, their productivity and earnings are a powerful force for poverty reduction. [Link]

It is argued that remittances play an important role in poverty alleviation because they go directly to people rather than to governments. This allows them to benefit families directly, unlike foreign aid, with little in the way of overhead being charged by the state. Remittances are also counter-cyclical, and so serve as an important form of social insurance.

However, remittances are used to fund consumption more than investment, which conditions their impact on poverty. Furthermore, in countries where remittances are coming from brain drain, the money goes to the elites within society, i.e. those who need it least. Remittances go to help the poor only in countries which export their poor such as Mexico which earns more foreign exchange from remittances than agriculture. Lastly, these large flows of remittances may be the artifact of relatively recent immigration:

An analysis of the 2000 US census reveals that of the foreign population in the United States in that year, nearly half (47%) entered the country in just the previous decade. [Link]

As immigration regulations are tightened, existing migrants may start to send back less money over time and remittance flows may lessen. In that case, this surge in remittances may prove to be the result of a post-Cold War temporary opening in borders, and not something that poor countries can rely on long term.